Field emission mechanism from undoped chemical vapor deposition diamond films

We have investigated the field emission mechanism for nominally undoped dia mond films with a thickness ranging from 3.2 to 27.5 mu m, epitaxially grow n on low p-doped Si(001). The experiments were performed in a field emissio n scanning microscope, which allows the investigation of mu m-sized spots o n cm(2)-sized samples. First, all samples were heated at 300 degrees C, res ulting in electrically insulating properties. Then, current I versus voltag e U measurements in electrode contact mode were performed at different temp eratures and for both polarities as well as in noncontact mode for differen t electrode gaps. For local current densities up to 0.5 A/cm(2) the field e mission was limited by the diamond bulk properties and not by the surface b arrier. Conduction through the bulk occurred by a Poole-Frenkel process for traps with overlapping Coulomb potentials. A thermally assisted electron h opping over the Coulomb barriers was proven and an activation energy of 0.4 3 eV and a trap density of 7.1 X 10(18)/cm(3) were derived. (C) 2000 Americ an Vacuum Society. [S0734-211X(00)05002-2].